1. Field of the Invention
This invention relates to a method of cleaning solid elements, such as moulds, and more especially the cleaning of glassmaking moulds.
2. Discussion of the Background
Although the invention concerns other industries, its explanation will be limited to the cleaning of glassmaking moulds. Glassmaking moulds, notably those used for the production of bottles or flasks, are of several types; they may be, for example, roughing moulds and finishing moulds. These moulds operate most commonly at very high production rates, that is to say they produce a large number of bottles or flasks very rapidly. During manufacture these moulds and, more particularly, the zones that come into contact with the glass, are treated with agents such as greases. Consequently, this type of mould becomes dirty very rapidly and therefore must be regularly cleaned to give finished products of good quality.
In glassworks operating at the usual high rates, the roughing moulds are cleaned approximately every two days and the finishing moulds approximately once a week.
The techniques commonly used for cleaning glassmaking moulds are of the mechanical type. Sandblasting or indeed polishing techniques, for example, may be used. It appears that these techniques are entirely satisfactory from the cleaning aspect, and enable the entire layer of dirt which becomes deposited during use to be removed.
In contrast, it has become apparent that these treatments are generally too severe. In fact, simultaneously with the removal of the dirt, this type of treatment damages the metal of which the mould is made. Such damage of the mould, which corresponds at each cleaning to an erosion of approximately 10 microns from the surface of the mould, has harmful consequences.
In fact, the size of the cavity or indentation, that is the place where the product is formed, is increased, which leads either to a greater consumption of glass for an equivalent product or a variation in the capacity of the article for a constant consumption of glass. The external dimensions of the articles are also modified and no longer meet the requirements. Furthermore, these deformations lead to problems of demoulding which generally result in defects or breakage of the finished products. Most commonly, the finished products have a surface state which degrades with the aging of the mould. These disadvantages lead to maintenance costs for repairing the moulds which are generally high and to premature replacement of these moulds.
The French Patent published under number 2 641 718 describes a cleaning method which enables different types of dirt on surfaces, for example metal surfaces, to be removed without wear or degradation of the metal. This is a technique of photo-ablation by laser impact. Tests have shown that the application of this method to the cleaning of glassmaking moulds enables the film of dirt to be effectively removed without degradation of the surface of the mould. On the other hand, the application of this method to the cleaning of moulds does possess disadvantages which make it unacceptable from an industrial aspect. In fact, the time necessary for performing the cleaning of a mould by this method is too long and cannot be reconciled with the production rates necessary for cleaning glassmaking moulds.
The moulds have, in addition, geometries that are frequently complicated, which make them difficult to clean by a laser beam which cannot reach all the corners and, notably, the grooves and fins present on the outer surface of the mould. The regions of the moulds that enable the different parts of which the moulds are made to be fitted and hooked together are also very difficult of access by a laser beam. The cleaning of these regions by such a technique would necessitate difficult handling operations which by their nature are relatively slow.